An electromechanical power transmission chain comprises typically one or more electrical machines and one or more electronic power converters. The electromechanical power transmission chain can be a series transmission chain where one of the electrical machines operates as a generator and the one or more electronic power converters are arranged to convert the voltages produced by the generator into voltages having amplitudes and frequencies suitable for the one or more other electrical machines. The generator can be driven with a combustion engine that can be e.g. a diesel engine, an Otto-cycle engine, or a turbine engine. The other electrical machines can be, for example, electrical motors arranged to drive wheels, chain tracks, and/or other mechanical loads. An electromechanical power transmission chain can be as well a parallel transmission chain where an electrical machine that is mechanically connected to a combustion engine operates sometimes as a generator which charges a storage circuit for storing electrical energy and sometimes as a motor that receives electrical energy from the storage circuit and assists the combustion engine when high mechanical output power is needed. It is also possible that an electromechanical power transmission chain is a combined series-parallel transmission chain so that one or more electrical machines are mechanically connected both to a combustion engine and to a mechanical load and one more other electrical machines are configured to drive other mechanical loads in the same way as in a series transmission chain.
Electromechanical power transmission chains of the kind described above provide advantages compared to a traditional mechanical power transmission chain because, for example, the operation area of the combustion engine can be more freely selected from the viewpoint of the operational efficiency of the combustion engine, and thus savings in the fuel costs can be achieved. In parallel transmission chains the operation area of the combustion engine cannot be, however, chosen so freely as in series transmission chains because in a parallel transmission chain an electrical machine is mechanically connected both to a combustion engine and to a mechanical load and thus the required rotational speed of the mechanical load dictates also the rotational speed of the combustion engine. The fuel consumption of the combustion engine tends to increase especially in such peak-load situations where the power demand of the mechanical load is above a power range where the combustion engine operates at, or at least near to, its optimal operational efficiency.